MAC Address Tables with Multiple Switches
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Finally, to complete the discussion, it helps to think about an example with multiple switches,
just to emphasize how MAC learning, forwarding, and flooding happens independently
on each LAN switch.
Consider the topology in Figure 7-10, and pay close attention to the port numbers. The
ports were purposefully chosen so that neither switch used any of the same ports for this
example. That is, switch SW2 does have a port F0/1 and F0/2, but I did not plug any devices
into those ports when making this example. Also note that all ports are in VLAN 1, and
as with the other examples in this chapter, all default configuration is used other than the
hostname on the switches.
Figure 7-10 Two-Switch Topology Example
Think about a case in which both switches learn all four MAC addresses. For instance, that
would happen if the hosts on the left communicate with the hosts on the right. SW1’s MAC
address table would list SW1’s own port numbers (F0/1, F0/2, and G0/1), because SW1 uses
that information to decide where SW1 should forward frames. Similarly, SW2’s MAC table
lists SW2’s port numbers (F0/3, F0/4, G0/2 in this example). Example 7-8 shows the MAC
address tables on both switches for that scenario.
Example 7-8 The MAC Address Table on Two Switches